A hologram is an object of the wave front of an object light recorded on a photosensitive material as interference fringe by interference of two lights (object and reference lights) of the same wavelength. When a light of the same wavelength as the reference light used during interference fringe recording is irradiated, the interference fringe induces a diffraction phenomenon, and the wave front identical with that of the original object light may be reproduced. Since the holograms have many advantages such as favorable appearance and relative difficulty in copying, the holograms are used in, for example, forgery prevention applications.
Example of a known method for using a hologram is a method of reproducing an optical image by causing a hologram to transmit or reflect a reference light.
For example, Patent Literature 1 discloses carrying out an authenticity determination by using an optical image reproduced by projecting diffracted light reflected by a laser reflection type hologram onto a screen.